There have been used various transparent or semi-transparent polyethylene films, ethylene-vinyl acetate copolymer films or soft vinyl chloride resin films for the covering of houses or tunnels or covering ground for crop plantation in the planting of vegetables, flowers, fruit trees, and the like. In covering houses and tunnels, they are used for the purpose of promoting the growth of crops while maintaining the temperature within the houses and tunnels in the low temperature season and of saving energy for heating the houses in the very cold season. The covering of the ground for crop plantation, so-called "mulching", is usually applied to retain moisture in the soil, to raise the undergound temperature, and to prevent loss of fertilizer components, and so on.
With the recent popularity and progress of the above cover culture, there occurs a severe problem of damage to crops by harmful insects. Particularly, in warm regions such as Okinawa, Kyushu and Shuikoku, damage by thrips (e.g. Thrips palmi), aphides (e.g. Aphis gossypii, Mizus persieae), etc. has become a very severe problem.
In order to remove or prevent such damage, it has been proposed to use agricultural chemicals such as repellents, insecticides, etc. or to trap or catch them with ferromone which is effective for attracting insect pests, or with colored tapes, and some methods have practically been used.
However, these methods have some problems. For instance, agricultural chemicals face a problem of the occurrence of resistant insect pests by the use thereof for a long time, and hence, other chemicals having stronger insecticidal activity must be developed, which results occasionally in an increase of toxicity to humans and secondary pollution such as environmental pollution due to the increased deposition of toxic chemicals in soil, and the like.
There have also been proposed other methods for removal of insect pests without problems as mentioned above, for instance, covering of film having a high reflectivity of sunlight (e.g. an aluminum-deposited film, etc.) on the culture crops or ground, by which the entrance of flying insects is prevented, or by preventing the houses or tunnels from flying insect pests by means of covering the horses and tunnels with a film which can cut off close ultraviolet rays, and some of the methods have already been practiced.
However, among the above methods, the former method entails unfavorably high costs and further is not suitable for covering houses or tunnels because of lower light permeability notwithstanding its high light reflectivity, and even in mulching of culture ground, the underground temperature is slightly raised, and hence, it is not practically used for crop cultures other than some specific utilities which utilize these characteristics. Moreover, although the latter method is excellent for the removal of insect pests within the covered houses and tunnels, it affects the growing of eggplant or coloring of flowers, and hence, it is limited in its applications. Also, it exhibits no effect for the prevention of insect pests in the case of mulching.